Method for producing alloys having wear-resistant surfaces

ABSTRACT

Alloys having wear-resistant surfaces are produced by incorporating in the molten matrix metal wear-resistance imparting components with a specific gravity lower or higher than the specific gravity of the matrix metal and centrifugally casting the resulting alloy in the form of a hollow cylinder whereby the component, if lighter, is concentrated in the inner surface portion of the cylinder wall, or, if heavier, the component is concentrated in the outer surface portion of the cylinder wall. Work pieces, such as sealing strips for rotary piston engines, may be formed from selected portions of these cylinders.

United States Patent 1 Beyer et al.

[451 Dec. 30, 1975 METHOD FOR PRODUCING ALLOYS HAVING WEAR-RESISTANT SURFACES [75] Inventors: Horst Beyer; Hans-Jiirgen Veutgen,

both of Burschcid, Germany [30] Foreign Application Priority Data July 6, 1972 Germany 2233148 [52] US. Cl 164/58; 164/114 [51] Int. Cl. B22D 27/18 [58] Field of Search 164/58, 97,114, 57; 75/123 CB [56] References Cited UNITED STATES PATENTS 727,103 5/1903 Davis 164/58 2,684,900 7/1954 Webbere 75/123 CB 3,330,651 7/1967 Younkin 75/123 CB 3,695,865 l0/l972 Wolker........ 75/123 CB X 3,767,386 10/1973 Ueda et al. 75/123 CB X Primary ExaminerFrancis S. Husar Assistant Examiner-John E. Roethel Attorney, Agent, or FirmSpencer & Kaye [57] ABSTRACT Alloys having wear-resistant surfaces are produced by incorporating in the molten matrix metal wearresistance imparting components with a specific gravity lower or higher than the specific gravity of the matrix metal and centrifugally casting the resulting alloy in the form of a hollow cylinder whereby the component, if lighter, is concentrated in the inner surface portion of the cylinder wall, or, if heavier, the component is concentrated in the outer surface portion of the cylinder wall. Work pieces, such as sealing strips for rotary piston engines, may be formed from selected portions of these cylinders.

14 Claims, No Drawings METHOD FOR PRODUCING ALLOYS HAVING WEAR-RESISTANT SURFACES BACKGROUND OF THE INVENTION The present invention relates to a method for producing alloyed materials with wear-resistant surfaces suitable particularly for the production of cast-iron sealing strips for rotary piston engines.

A number of wear-resistant metallic materials are known, both ferrous and nonferrous. Such wear-resistant alloys in all cases have a relatively soft but tough matrix in which the wear-resistant phases, such as carbides, nitrides or hard metallic compounds, are embedded.

These wear-resistant particles solidify from the melt and are uniformly distributed throughout the article in the usual casting procedures. If the number of wearresistant particles in the surface portions of such cast pieces is to be increased, it is necessary to do so throughout the casting and this is possible only to the extent permitted by the phase diagram of the particular alloy which more or less corresponds to the equilibrium state.-

Since these wear-resistant particles are frequently carbides or compounds of relatively expensive elements such as, for example, tungsten, vanadium, niobium etc., the further addition of such elements to the alloy even if it were possible according to the phase diagram would substantially increase the ultimate cost. In a wear-resistant cast-iron material in which, due to its dry running properties, unbound carbon is to be maintained in the structure, only a very slight concentration of such elements is permitted since otherwise there will result substantially complete carbidic hardening with consequent difficulties inv the machining, particularly by cutting or milling procedures. This is particularly disadvantageous where only one surface or edge of a piece is intended to have wear-resistant properties.

It is also known that in the centrifugal casting of metals c'ertain components tend to deposit at the inner or outer surfaces under the influence of centrifugal forces. Thus, during centrifugal casting, slag and gas inclusions usually are deposited on the inside according to their lower specific gravity. On the other hand, the outer layers disposed near the edge of the mold will harden faster in the centrifugal casting process. Consequently the structure here becomes finer and thus harder. For a more detailed description of such phenomena, reference is made to Englisch, Kolbenringe [Piston Rings], pp. 205, 206, 1958 edition, published by Springer Verlag.

It is further known in the centrifugal casting of cylinder liners that several types or iron or steel can be cast in succession. Thus, for example, the outer layer of such liners can be of an inexpensive conventional cast iron, while the inner layer is a more wear-resistant cast iron. The structural configuration of each layer is thus uniformly distributed over the entire cross section. Such a procedure is described in German Pat. No. 937,024 of Aug. 31st, 1949.

Wear-resistant layers can also be applied to materials by a flame spraying process, for example. In contradistinction thereto, the process according to the present invention permits the material and the wear-resistant surface to be prepared in a single casting, thus being less expensive, and it is possible in this way to have graphite available in addition to the hard components to obtain anti-friction properties, which is not possible in such spray procedures due to the oxidative destruction.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a process for producing materials which are wear-resistant only at their surfaces. It is a further object of this invention to minimize the amount of relatively expensive additives in the alloy article while optimizing the surface concentration in the wear-resistant region. It is a further object to have the wear-resistant surface contain enough graphite only for anti-friction properties. It is another object of this invention that the material be capable of being machined by cutting or milling, with grinding being required only in the region of the carbidic deposit of the wear-resistant surface so that sealing strips for rotary piston engines can be cut out of this region.

These and other objects will be apparent from the following description of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is based on the fact that materials which contain components forming hard phases with one another which components deposit simultaneously during cooling according to the phase diagram, form hard layers during solidification of the melt and under the simultaneous influence of centrifugal forces and cooling. These phases are deposited on the inside in alloys where they have a lower specific gravity than the surrounding matrix, and will be deposited toward the outside where their specific gravity is higher than that of the matrix. Thus, by selection of the particular alloying components and control of the temperature, cooling rates and other operating conditions, the wearresistant properties can be developed at the inner or the outer tubular wall as desired.

This principle can be used to produce ferrous metal tubes by the centrifugal casting process. The basic ferrous metal or matrix is alloyed with hard-substance forming materials, such as titanium, vanadium, niobium, tantalum or tungsten. Depending on the selected centrifugal and hardening conditions, these substances are concentrated on the surface of the tube, either the inside or the outside, as carbides, nitrides or borides, depending on their specific gravity, so that tubes with predetermined wear-resistant surfaces are produced. The presence of such wear-resistant phases can be determined by chemical analysis, physical analysis or from a photomicrograph of a ground surface, according to conventional procedures. Other known alloying elements such as copper, nickel or tin, which do not lead to the formation of carbides, nitrides or borides, can be added to modify the properties of the basic metal.

From a pipe or tube so prepared, sections can readily be removed for fabrication of articles, for example sealing strips for rotary piston engines, wherein the zone of maximum wear-resistant alloy concentration will be situated in the portion of the article to be subjected to the maximum wear or contact with other elements in use.

Depending upon the composition of the' basic or matrix alloy, the proportion of the added substance to produce the desired wear-resistant layer may vary from 3 about 0.3% to about 5.0% of the final mixture to be cast.

EXAMPLE 1:

A melt of cast iron alloy which is martensitic in the cast state and contains 3.25% carbon 2.48% silicon 1.02% manganese 0.29% phosphorus 0.049% sulphur 0.62% chromium 1.24% molybdenum 0.23% vanadium 1.16% copper 0.54% nickel 0.62% tungsten 0.08% tin was further alloyed with titanium to a content of 1.0%, and a pipe was centrifugally cast from this melt.

For this purpose, the melt of the cast iron is heated to 1,350 to 1,450 C and chilled into an iron mold which has the temperature of 400 to 600 C and the form of a tube with a diameter of 294 mm. In case of a rotation of about 500 revolutions per minute the melt of the cast iron solidifies by forming an iron tube. Five minutes later, the cast iron tube is cooled down to about l,000 C so that the rotation may be stopped and the cast tube can be removed.

In the following hardening process, the cast iron tube is annealed for one hour at 820 to 950 C and then quenched in oil. Then the cast tube is tempered in air for one hour at about 300 to 500 C.

The resulting pipe was martensitic, with an outer zone hardness of Hv 584-623 kp/mm while the inner surface had a hardness of Hv 666-713 kp/mm the inner region being highly enriched with carbides and nitrides.

Inspection and analysis revealed that while the titanium content averaged 1.0% across the cross section of the pipe, it was 0.34% at the outer wall and 4.11% at the wear-resistant surface. Titanium appears principally as the carbide although some of it may be in the form of the nitride. Graphite appears in sufficient quantities at the wear-resistant surface to provide the desired anti-friction properties.

During the subsequent tempering treatment the hardness of the matrix material decreased to about Hv 350 kp/mm corresponding to that of the outer zone, thus permitting easy machining. Following tempering, the hardness of the inner layer decreased slightly to about HV 600 kp/mm since the carbides and nitrides do not decompose under these conditions.

It is thus evident that the invention provides a simple and effective procedure for the preparation of alloy materials having a wear-resistant surface, which can be readily fabricated into wear-resistant parts or elements essentially by machining with little or no grinding. In comparison with known alloy materials for such uses, alloy materials are produced according to this invention at substantially less cost due to the small quantities of expensive additives which are required. In addition,

4 the wear-resistant surface contains the graphite whic' is necessary in machine parts which are subjected to sliding wear.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. Process for producing materials with wear-resistant surfaces, comprising forming a melt of a matrix material and at least one substance which forms at least one hard solid phase having a density other than that of the matrix material and which separates from the basic matrix material during hardening, casting the resulting melt and subjecting the molten casting to mass acceleration during the hardening process.

2. Process as defined in claim 1 wherein the melt is centrifugally cast into a pipe.

3. Process as defined in claim 1 wherein iron is used as the matrix material, said iron containing enough carbon that graphite must occur during hardening in addition to the hard solid phase.

4. Process as defined in claim 2 wherein machine parts with wear-resistant surfaces can be worked out of said pipe.

5. Process as defined in claim 1 wherein the added substance is one which combines with carbon, nitrogen, or boron to form the wear-resistant hard solid phase.

6. Process as defined in claim 5 wherein the added substance is a metal selected from the group consisting of titanium, vanadium, niobium, tantalum, and tungsten.

7. Process as defined in claim 1 wherein the added substance is added in an amount of 0.3 to 5.0% of the final alloy.

8. Process as defined in claim 3 wherein the added substance is a metal selected from the group consisting of titanium, vanadium, niobium, tantalum, tungsten, copper, nickel and tin.

9. Process as defined in claim 4 wherein the machine parts are sealing strips for rotary piston engines.

10. Process as defined in claim 1 wherein the wearresistant surface if formed on the inside surface of the cast matrix material.

11. Process as defined in claim 1 wherein the wearresistant surface is formed on the outside surface of the cast matrix material.

12. Process as defined in claim 1 wherein the added substance it titanium, and is present at the inner surface in an amount higher than at the outer surface.

13. Process as defined in claim 12 wherein the titanium content through the cross section of the cast matrix material averages 1%, the titanium content at the outer surface is 0.34%, and the titanium content at the inner surface is 4.11%.

14. Process as defined in claim 13 wherein graphite appears at the inner surface to provide anti-friction properties. 

1. Process for producing materials with wear-resistant surfaces, comprising forming a melt of a matrix material and at least one substance which forms at least one hard solid phase having a density other than that of the matrix material and which separates from the basic matrix material during hardening, casting the resulting melt and subjecting the molten casting to mass acceleration during the hardening process.
 2. Process as defined in claim 1 wherein the melt is centrifugally cast into a pipe.
 3. Process as defined in claim 1 wherein iron is used as the matrix material, said iron containing enough carbon that graphite must occur during hardening in addition to the hard solid phase.
 4. Process as defined in claim 2 wherein machine parts with wear-resistant surfaces can be worked out of said pipe.
 5. Process as defined iN claim 1 wherein the added substance is one which combines with carbon, nitrogen, or boron to form the wear-resistant hard solid phase.
 6. Process as defined in claim 5 wherein the added substance is a metal selected from the group consisting of titanium, vanadium, niobium, tantalum, and tungsten.
 7. Process as defined in claim 1 wherein the added substance is added in an amount of 0.3 to 5.0% of the final alloy.
 8. Process as defined in claim 3 wherein the added substance is a metal selected from the group consisting of titanium, vanadium, niobium, tantalum, tungsten, copper, nickel and tin.
 9. Process as defined in claim 4 wherein the machine parts are sealing strips for rotary piston engines.
 10. Process as defined in claim 1 wherein the wear-resistant surface if formed on the inside surface of the cast matrix material.
 11. Process as defined in claim 1 wherein the wear-resistant surface is formed on the outside surface of the cast matrix material.
 12. Process as defined in claim 1 wherein the added substance it titanium, and is present at the inner surface in an amount higher than at the outer surface.
 13. Process as defined in claim 12 wherein the titanium content through the cross section of the cast matrix material averages 1%, the titanium content at the outer surface is 0.34%, and the titanium content at the inner surface is 4.11%.
 14. Process as defined in claim 13 wherein graphite appears at the inner surface to provide anti-friction properties. 